1. Field of the Invention
The present invention relates generally to oil field cement fluid loss control additives, and more particularly, to field prepared liquid fluid loss control additives for use in oil field cement compositions.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in completion and other operations carried out in oil and gas wells. The hydraulic cement compositions utilized are normally field prepared, i.e., prepared at or near the job sites, just prior to their use. Such field preparation generally comprises producing a pumpable slurry at the well site comprising a hydraulic cement, water and various additives. The slurry is then pumped into a subterranean zone to be cemented by way of the well bore penetrating the zone. After placement in the zone, the cement slurry sets into a hard mass.
Hydrophilic polymers have heretofore been utilized as oil field cement composition additives for reducing fluid losses from cement compositions to surrounding subterranean formations as the compositions are being placed or after placement and prior to setting. In primary oil well cementing, a cement composition is placed in the annulus between a casing or liner and the well bore to seal the annulus and bond the casing or liner to the earth formations penetrated by the well bore. If the cement composition loses appreciable fluid, i.e., water, to the earth formations, then premature gelation of the cement composition and bridging of the annulus before proper placement of the cement composition can result. In secondary cementing operations, i.e., remedial cementing operations, the control of fluid loss from cement compositions is necessary to achieve the precise cement composition placement required in such operations.
The hydrophilic polymers commonly utilized as fluid loss agents in cement compositions are dry particulated solids. If such hydrophilic polymers are mixed directly with hydraulic cement and water, and great care and special mixing techniques and apparatus are not utilized, then agglomerated masses known in the art as gel balls and/or fish eyes can be formed. Once formed, gel balls and fish eyes are very difficult to break up and dissolve.
In order to obviate such problems, liquid fluid loss control additives containing hydrophilic polymers have been developed and utilized heretofore. For example, U.S. Pat. No. 4,687,516 issued Aug. 18, 1987 discloses liquid fluid loss control additives for oil field cements which have long storage lives without excessive settling and which can be mixed with cement slurries without the formation of gel balls or fish eyes. While such liquid fluid loss control additives have been made and used successfully, they suffer from the disadvantage that they must be prepared at a location remote from the oil field, transported to warehouses and stored. When used, the liquid additives are transported from storage to well sites in containers and mixed with cement compositions prepared at the sites. While such liquid fluid loss control additives have long storage lives without excessive settling, some settling does take place over extended lengths of time and when too much settling has occurred, difficult and costly reprocessing is required.
The hydrophilic polymer or polymers contained in the heretofore used liquid fluid loss control additives are also commonly utilized directly to form gelled aqueous fluids used in carrying out oil and gas well stimulation and other operations. The hydrophilic polymers in solid form are therefore generally available at well sites. Thus, there is a need for methods of utilizing solid hydrophilic polymers as fluid loss control additives for oil field cements to eliminate the requirement that preformed liquid fluid loss control additives containing such hydrophilic polymers must be stored and transported to the well site and to eliminate the requirement that special mixing techniques and elaborate apparatus must be used for directly mixing the solid hydrophilic polymers with the cements.